Polybenzoxazole (PBO), polybenzimidazole (PBI) and polybenzothiazole (PBT) and related polymers (hereinafter referred to as PBZ polymers) are known polymers which can be extruded as fibers of films having a high tensile strength and high tensile modulus which are useful for structural applications. It is known in the art to synthesize PBZ polymers by the reaction of a first monomer having a primary amine group and a hydroxy, thio or amine group bonded to an aromatic group in ortho position with respect to each other, and a second monomer having an "electrondeficient carbon group". Known electron-deficient carbon groups are set out in Table I hereinafter.
TABLE I ______________________________________ --COOH --CSSH --COBR --CSI --CSOH --COCO --CSBR CONHR.sub.1 --COSH --CSCO --COI --CS --CN ______________________________________
See, e.g., Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986); Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985); Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985), which are incorporated herein by reference.
In most commonly used monomers, the electrondeficient carbon group is either a carboxylic acid group or a carboxylic acid halide group. For instance, monomers may be 4-hydroxy-5-aminobenzoic acid, terephthalic acid, or terephthaloyl chloride.
Several problems are associated with the known monomers. Acids such as terephthalic acid are highly insoluble in solvents which will dissolve the polymer, so that they must be micronized to produce PBZ polymers of high molecular weight. Acid chlorides such as terephthaloyl chloride are moisture sensitive and can sublime easily. What is needed is a process to synthesize PBZ polymers using monomers having electrondeficient carbon groups which are not moisture sensitive and do not require physical micronization prior to their use in the reaction.